Use of monoclonal antibody in diagnosis of candidiasis caused by Candida albicans: Detection of circulating aspartyl proteinase antigen

To develop a serological diagnosis of invasive candidiasis based on detecti on of circulating secreted aspartyl proteinase (SAP) antigen of Candida alb icans, three different enzyme-linked immunosorbent assays (ELISAs) were com pared. The first was a standard ELISA to detect anti-SAP antibodies, and th e others were an antigen capture ELISA and an inhibition ELISA to detect ci rculating SAP antigen with monoclonal antibody (MAb) CAP1, which is highly specific for SAP. These tests were applied to 33 serum samples retrospectiv ely selected from 33 patients with mycologically and/or serologically prove n invasive candidiasis caused by C. albicans. Serum samples from 12 patient s with aspergillosis and serum samples from 13 healthy individuals were als o included. The sensitivities and specificities were 69.7 and 76.0% for the standard ELISA and 93.9 and 92.0% for the antigen capture ELISA, respectiv ely. However, these values reached 93.9 and 96.0%, respectively, for the in hibition ELISA. Serum samples from 31 of 33 patients had detectable SAP ant igen, dth concentrations ranging from 6.3 to 19.0 ng/ml. These results indi cate that the inhibition ELISA with MAb CAP1 is effective in detection of c irculating SAP antigen and that this assay may be useful for diagnosis and treatment monitoring of invasive candidiasis.